Hi,
Try to implement SPF/DKIM/DMARC to avoid being caught as a spamer.
The DNS TXT record should be like that :
Host : _dmarc
type : TXT
Value : = DMARC1; p=none; rua=mailto:entreprise1@youremailhere; ruf=mailto:entreprise1@youremailhere; fo=1;
Change the mailto email by your email adresse.
On this email adresse you will receive XML reports that you can analyze to know who is sending emails on behalf of your domain and make sure all your e-mails are well authenticated with SPF/DKIM.
When this is done you can protect your domain with DMARC quarantine policy like this one :
Host : _dmarc
type : TXT
Value : = DMARC1; p=quarantine; rua=mailto:youremailhere; ruf=mailto:youremailhere; fo=1;
By adding this DMARC value, any emails sent with your email addresses that is not authenticated will be sent to the spam folder of the recipient. But your authenticated emails will have much more chance to be qualified as “good mail”. Many factors will determine whether your emails will be qualified as spams. Don’t underestimate technical and content criterias that antispams are using to flag you email as a spamer.
Retex on how to implement DMARC in big firm there (french sorry) :link here